Issues with using Third Party .Net client library in Xamarin

I m trying to use Apache Chemistry DotCMIS client library for .NET with Xamarin in order to integrate with Alfresco repository. I read in xamarin documentation "We cannot use off-the-shelf .NET assemblies without recompiling the C# source against the Xamarin Mobile profile". So i downloaded the DotCMIS client source(https://chemistry.apache.org/dotnet/dotcmis.html),imported in Xamarin Studio followed by doing Build project in xamarin studio.

I am getting below error:

/Downloads/chemistry-dotcmis-0.5-src/src/enums.cs(30,30): Error CS1110:

DotCMIS.Enums.CmisValue.GetCmisValue(this System.Enum)': Extension methods
require

System.Runtime.CompilerServices.ExtensionAttribute' type to be available. Are you missing an assembly reference? (CS1110) (DotCMIS)

I m a newbie to .Net world and Xamarin world. Please help me with this as i am stuck here.